Photoelectrochemical Degradation of 17-β Estradiol Using a Photoanode Prepared with RuO2 Nanoparticles Supported over Graphene

The development of photoelectroactive materials has been a target of several researches on the removal of environmental pollutants. In this sense, the use of semiconductors materials with small band gap energies has been used as modifiers materials with photoelectrochemical properties providing visible light activation and decreasing the electron-hole recombination. Reduced graphene oxide (RGO) is a single layer of hybridized carbon atoms that has attracted attention due to their electronic and structural characteristics as a semiconductor type p. Besides RGO can act as a support for immobilization of several species. One special substance used as a RGO modifier is ruthenium oxide (RuO₂) nanoparticles. These oxide are recognized for their excellent electrocatalytic activity for oxygenated species, and can be easily adsorb over RGO basal plane. It has been observed that RGO/RuO₂ has the excellent catalytic properties for degradation of organic pollutants and can convert the solar light into hydrogen, as the concept of water splitting. Also, the system RGO/RuO₂ makes a heterojunction p-n, decreasing the recombination electron-hole. The objective of this work is the synthesis, characterization and application of a photoanode based on a RuO₂ supported on RGO for the photoelectrochemical degradation of 17β-estradiol. The material was prepared by a single mixture of RGO and ruthenium chloride in purified water. The mixture was kept under hydrothermal system assisted by microwave at 160 ºC during 15 minutes. Thus, a suspension containing 5.0 mg RGO/RuO₂ in 1.0 mL of ethanol with 0.5 % of Nafion was dropped over a glassy carbon plate. The structural and morphologic characteristics of the RGO/RuO₂ nanoparticles were carried out using transmission microscopy (TEM), X ray diffraction (DRX) and microanalysis using EDX. The structural and morphological characterization demonstrated that the RuO₂ nanoparticles was well-dispersed over the RGO surface and the nanoparticles with monoclinic phase have an average diameter at 4.0 nm. The prepared material was electrochemical characterized using linear sweep voltammetry (LSV) in phosphate buffer solution pH 7.0 containing 50 µmol L^-1 of 17β-estradiol. The LSV demonstrated that the RGO/RuO₂ surface allowed a 17β-estradiol oxidation peak at 0.65 V vs. Ag/AgCl. The observed value of the current peak in presence of solar light increased in almost 2-fold compared with the photoanode in dark. The photoanodes were then used in a photoelectrochemical system on the oxidation 17β-estradiol under visible irradiation by a high Xe lamp (250 W). The hormone degradation was monitored by spectrophotometric, total organic carbon (TOC) measurements and liquid chromatography (HPLC). The best experimental conditions promoted a removal at 90.5 % of the 17β-estradiol after 180 minutes of photoelectrocatalytic treatment under pseudo first order kinetics. Therefore, the use of RGO/RuO₂ as a material for development of photoelectrochemical method could be a promising alternative for the remediation of endocrine disruptor in environmental.

Aknowledge: FAPESP